1. Field of the Invention
The present invention relates to a film deposition method that deposits a reaction product of at least two kinds of reaction gases that react with each other by alternately supplying the gases onto the substrate, and more specifically to a film deposition method appropriate for filling a concave portion formed in a surface of the substrate with the reaction product.
2. Description of the Related Art
A process of fabricating a semiconductor integrated circuit (i.e., IC) includes a process of depositing a thin film on a semiconductor wafer. With respect to this process, improvement of uniformity within a surface of the wafer is desired to answer demands for further miniaturization of the IC. A deposition method called an atomic layer deposition (ALD) method or a molecular layer deposition (MLD) method is expected to respond to such demands. In the ALD method, by repeating a cycle of adsorbing one reaction gas (e.g., a reaction gas A) of two kinds of reaction gases that react with each other on a surface of a wafer, and of reacting the other reaction gas (e.g., a reaction gas B) with the adsorbed reaction gas A, a thin film made of the reaction product is deposited on the wafer. The ALD method has advantages of having superior film thickness uniformity and film thickness controllability for utilizing adsorption of the reaction gases on the surface of the wafer.
There is a turntable-type film deposition apparatus as one of the film deposition apparatuses that implement the ALD method, as disclosed in Japanese Patent No. 4661990. This film deposition apparatus includes a turntable rotatably provided in a vacuum chamber and on which a plurality of wafers is placed, a separation area separating a supply area of the reaction gas A and a supply area of the reaction gas B that are zoned above the turntable, evacuation openings provided respectively corresponding to the supply areas of the reaction gases A and B, and an evacuation device connected to these evacuation openings. In such a film deposition apparatus, the wafer passes through the supply area of the reaction gas A, the separation area, the supply area of the reaction gas B, and the separation area in sequence. This allows the reaction gas A to be adsorbed on the surface of the wafer in the supply area of the reaction gas A, and the reaction gas B to react with the reaction gas A on the wafer and in the supply area of the reaction gas B. Because of this, the reaction gas A and the reaction gas B do not have to be switched during the deposition, and can be supplied continuously. Accordingly, an evacuation/purge process is not required, which can advantageously reduce deposition time.
However, sometimes the reaction gas B cannot sufficiently react with the reaction gas A while the wafer passes the supply area of the reaction gas B. For example, when reactivity of the reaction gas A with the reaction gas B is low, a thin film may be deposited while leaving the reaction insufficient. Such a thin film contains a lot of unreacted molecular species or unbonded valance electrons, which may unfortunately deteriorate the deposited thin film. Moreover, when depositing a substance that widely changes its properties according to a deviation from stoichiometric composition of the reaction product, a problem of not being able to make the properties uniform may be caused.